Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel injection, or delivery, uses a port injector for each cylinder to deliver fuel to respective cylinders. Another type of fuel injection uses a direct injector for each cylinder. Engines have also been described using more than one injector to provide fuel to a single cylinder in an attempt to improve engine performance.
One such example (U.S. 2007/0119422 A1) describes a flexible multiple-fuel engine using both port and direct injection, where different fuel types are provided to the injectors. For example, direct injection of ethanol may be used with port injected gasoline to address knock limitations, especially under boosted conditions. In this example, a desired setting for the various fuels may be predetermined using engine maps, and then adjusted based on feedback from a knock sensor. Specifically, the effective knock suppression of the fuels can be varied responsive to operating conditions to improve engine efficiency while meeting engine output requirements.
However, the inventor herein has recognized several issues with such an approach. As one example, the above predetermined settings for the fuel distribution may be set based on an average operator driving cycle, where knock sensor feedback is relied upon to address variation in the operator driving habits. In this case, aggressive drivers may consistently experience transient knock before the system can react to the knock sensor feedback and adjust the fuel injection location/composition to abate the engine knock. Additionally, conservative drivers may consistently experience less fuel economy gains than otherwise possible and/or unnecessarily high ethanol consumption rates.
To address this and other issues, one example approach uses a method for operating an engine in a vehicle, the method comprising: delivering a first fuel to a cylinder of the engine from a first injector, delivering a second fuel to the cylinder of the engine from a second injector, (where, for example, the second fuel has a greater heat of vaporization than the first fuel), varying a relative amount of the first and second fuel as an operating condition varies; and adjusting delivery of at least the second fuel based on a driver selected engine operating mode.
In this way, it is possible to adjust, for example, both predetermined fuel injection settings, as well as feedback gains, to better match the engine performance to the driver's selected mode. In the example of a performance mode setting, the predetermined settings can be adjusted to increase, at a given speed/load, compared to a fuel economy mode, usage of the fuel providing increased knock suppression capabilities and/or an increased heat of vaporization. As such, the system may rely less on knock sensor feedback to correct inadvertent knock during transient load changes by ensuring sufficient knock suppression is already present. Likewise, in the example of a fuel economy mode setting, the predetermined settings can be adjusted to decrease the knock suppression capabilities of the fuel injection, and rely more heavily on knock sensor feedback. As such, the system may conserve knock suppression capabilities until actually needed and use the information of the performance setting to predict reduced transients.